Displacement Sensors Lab Report

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Lab 4: Displacement

Sensors

P e n n s y l v a n i a S t a t e U n i v e r s i t y

M E 3 4 5 W

S e c t i o n 0 0 1

4 / 7 / 2 0 1 4

Joseph R. Felice

Table of Contents

Abstract ........................................................................................................................... i

Introduction ................................................................................................................... 1

Results and Discussion ................................................................................................ 3

Station A ...................................................................................................................... 3

Station B ...................................................................................................................... 4

Station C ...................................................................................................................... 5

Station E ...................................................................................................................... 6

Station F ...................................................................................................................... 7

Conclusion ..................................................................................................................... 8

References ..................................................................................................................... 9

Sample Calculations Appendix .................................................................................. 10

Graph Appendix .......................................................................................................... 11

Table Appendix ........................................................................................................... 13

i

Abstract

The purpose of this laboratory experiment is to test the various different types of

displacement sensors. Specifically, two different classifications of sensors known as

contact and non-contact sensors will be utilized in this study. Five different lab stations

labeled A, B, C, E and F will each have one displacement sensor selected from the

aforementioned categories. Stations B and E will house contact sensors whereas

stations A, C and F will be equipped with non-contact sensors. The latter stations will

also be accompanied by various samples of wood, steel and aluminum. These samples

are to be used in testing the responsiveness of the non-contact sensors to different

types of materials. The responsiveness of the contact sensors at stations B and E will

be analyzed through the displacement of the rod with respect its cylindrical shell. At

station E the speed at which the rod is displaced in the cylindrical shell will also be

observed at both slow and fast speeds. Tektronix DSO2002 oscilloscopes will measure

output voltage signals for the displacements of the wood, steel and aluminum samples

along with the rod displacements for the non-contact and contact sensors, respectively.

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Introduction

Displacement sensors are widely used throughout the engineering profession

both as an educational tool and in industry. Contact sensors are electromechanical

devices which require direct physical contact with an object in order to respond to its

presence. An example of a contact sensor is a switch. Limit switches are the most

common in industrial settings [1]. The most ordinary application for a limit switch is as a

presence sensor. There are three different categories of limit switches which are push

on button, push on flexible paddle and roller. Other sensors which are often used in

industry are classified as non-contact sensors.

Usually, non-contact sensors are transducers. Comprised of control circuits,

these transducers are able to operate as switches. There are three typical types of non-

contact sensors. These types of sensors are inductive proximity, capacitive proximity

and optical proximity sensors [1].

An inductive proximity sensor can only recognize electrically conductive

materials. A capacitive proximity sensor responds to the presence of mostly any

material provided such an object can be electrically charged. Optical proximity sensors

rely upon the reflective qualities of materials brought into the range of its light beam.

Target materials which are reflective will shine the light emitted from the optical sensor

back to that unit of the sensor, thus registering the presence of an object [1]. Another

type of sensor often used in industry is a contact sensor. A commonly used type of

contact sensor is the Linear Variable Differential Transformer (LVDT).

A mechanical displacement which occurs by the movement of a rod through a

casing lined with primary and secondary coils accompanied with insulation is the main

operation of an LVDT. The rod is non-magnetic and consists of a magnetic nickel-iron

core at its tip. This rod pushes the core through the center of the opening in the casing

sweeping over the coil configuration, hence yielding a linear function for the output

voltage versus displacement plot [1].

Another special type of sensor, called the Hall Effect sensor, operates in such a

way that the level of its responsiveness is dependent upon the proximity of a magnet

with respect to the actual body of the sensor. At first, the displacement of this magnet is

adjusted through the motion of a lever arm that brings the magnet in closer toward the

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Hall Effect sensor. The current in the sensor shifts to one end as the magnet

approaches the body of the sensor. This shift in current pattern is detected by contacts

at both sides of the sensor which recognize that the current is more heavily

concentrated on one end. The output voltage reading on a Hall Effect sensor is

proportional to the proximity of the magnet with the body of the sensor [1].

The applications of sensors in industry vary depending upon which purpose their

function is to serve in regard to a specific task. For instance, heavy-duty limit switches

can be used as a safety mechanism for operating machinery to protect the machinist

from harm in the event of a malfunction [2]. LVDT sensor are used in a wide variety of

applications including but not limited to aircraft, spacecraft, satellite as well as nuclear

installations [3].

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Results and Discussion

Station A

Aluminum Samples:

Range: 5.8 Volts

Supplied Voltage: 24 Volts

Sensitivity: 1.93 Volts/inch

Displacement: 3 inches

Sensor Type: Non-contact

Signal Type: Continuous

Image 1: Shown above is the voltage output for the aluminum bar. Displayed to the

right of the image are signal related measurements.

Range: 5.7 Volts






Image 2: Featured here is the voltage output for the aluminum plate. Displayed to the

right of the image are signal related measurements.

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Steel Sample:

Range: 5.8 Volts






Image 3: Above is a display of the voltage output for the steel sample. Displayed to

the right of the image are signal related measurements.

Wood Sample:

The wood sample at this station generated no output voltage reading on the

DSO2002 when placed in proximity of the sensor despite several adjustments made to

the VOLTS/DIV and SEC/DIV knobs. Various different displacements were tested,

each yielding no results. A source voltage of 24 volts was used for each trial.

Station B

Contact Sensor:

Range: 120 Volts


Sensitivity: 60 Volts/inch


Sensor Type: Contact


Image 4: Above is a display of the voltage output for the contact sensor.

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Station C

Aluminum Sample:

Range: 3.9 Volts



Displacement: 3.88 inches



Image 5: Above is a display of the voltage output for the aluminum plate.

Wood Sample:

Range: 4 Volts






Image 6: Above is a display of the voltage output for the wood sample

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Station E

Contact Sensor:

Range: 10 Volts




Estimated Average Speed: 0.625

inches/second



Image 7: Above is a display of the voltage output for the contact sensor at slow speed.

For this contact sensor there is no supplied voltage since the sliding motion of

the rod in the cylinder by itself is what is responsible for generating the output voltage

signal. Consequently, there is no sensitivity associated with this sensor. Sliding the rod

in and out at a slow speed estimated at 0.625 inches/second generates a discrete

output signal.

Range: 66 Volts




Average Speed: 1.25 inches/second



Image 8: Above is a display of the voltage output for the contact sensor at fast speed

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As aforementioned, since no voltage is supplied to this sensor there is an absence

of any sensitivity factor related to the output signal. Sliding the rod at a fast speed

estimated at 1.25 inches/second generates a continuous output signal.

Station F

Steel Sample:

Range: 20 Volts





Signal Type: Discrete

Image 9: Above is a display of the voltage output for the steel sample.

Wood Sample:

The wood sample at this station produced no output voltage signal on the

DSO2002 when placed in proximity of the sensor despite several adjustments made to

the VOLTS/DIV and SEC/DIV knobs. Various different displacements were tested,

each yielding no results. A source voltage of 24 volts was maintained during these

trials.

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Conclusion

In this lab both contact and non-contact sensors were utilized to enhance the

understanding of their various industrial applications. The non-contact sensors at

stations A, C and F were accompanied by wood, steel and aluminum samples. The

capacitive sensor at station A recognized the presence of both the steel and aluminum

samples, however, it is apparent that it registered the aluminum in less time than it did

the steel for a displacement of 3 inches.

Steel and aluminum samples at Station A generated continuous waveforms,

hence smooth variations in magnitude. Each of these samples reached the maximum

capability of the capacitive sensor output causing the displayed signal to level out at the

sensor’s saturation point of 5.8 volts. Since wood cannot provide the electrical charge

needed for recognition by a capacitive sensor no output voltage signal was generated.

The non-contact optical sensor at station C recognized both aluminum and wood

samples in nearly the same amount of time. The displacement for the aluminum

sample with respect to the sensor was 3.88 inches and for the wood sample was 3.6

inches. Both yielded similar output signals, 3.9 Volts and 4 Volts, for aluminum and

wood, respectively.

The inductive proximity sensor at station F registered the presence of the steel

sample but like station A did not recognize the wood sample. The displacement of the

steel from the sensor was the closest it was for any of the target objects with respect to

the other sensors in this lab at 0.0625 inches. This generated a discrete waveform.

The contact sensor at station B was an LVDT. At a displacement of 2 inches to

the right the rod yielded an output voltage signal of 60 Volts. Similarly, at a

displacement of 2 inches to the left as the rod was going further in the casing an output

voltage of -60 Volts was generated.

The LVDT contact sensor at station E required no source voltage since it relied

solely on induction to generate an output voltage signal. As the rod traveled through the

casing slowly at an estimated speed of 0.625 inches/second a continuous waveform

was produced. When the rod traveled fast through the casing at an estimated speed of

1.25 inches/second a continuous waveform was generated with peak-to-peak output

voltage amplitude (range) of 66 Volts.

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References

[1] ME 345W Lecture Notes, Spring 2014, “Displacement Sensors,” Slides 1-12. Penn

State University, Angel Course Webpage.

[2] Grainger, 2014, “Limit/Interlock Switches,” from

http://www.grainger.com/category/limit-interlock-switches/switches/electrical/ecatalog/N-

8gd.

[3] AST Macro Sensors, 2014, “Heat Build Platform,” from

http://www.macrosensors.com/lvdt_tutorial.html#.

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Sample Calculations Appendix

Station A Aluminum Bar Sensitivity

5.8 Volts/3 inches = 1.93 Volts/inch

Station E Estimated Average Speed Calculations

Slow

2.5 inches/4 seconds = 0.625 inches/second

Fast

2.5 inches/2 seconds = 1.25 inches/second

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Graph Appendix

Station A

Aluminum Bar/Plate Samples:

Graph 1: Shown above is the plot of voltage output vs. displacement for the aluminum bar sample at station A with the equation of the line displayed next to the plotted line.

Graph 2: Above is the plot of output voltage vs. displacement for the aluminum plate sample at station A with the equation for the function displayed next to the line.

y = -1.9333x

-7

-6

-5

-4

-3

-2

-1

0

0 0.5 1 1.5 2 2.5 3 3.5

Capacitive Sensor Output

(volts)

Displacement (inches)

Voltage Output vs. Displacement

y = -1.9x

-6

-5

-4

-3

-2

-1

0

0 0.5 1 1.5 2 2.5 3 3.5


(volts)



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Steel Sample:

Graph 3: Featured above is the graph of output voltage vs. displacement for the steel sample at station A along with the equation for the line.

Graph 4: Featured above is the graph of output voltage vs. displacement for LVDT sensor sample at station B along with the equation for the line. Negative values for inches indicated that the rod was being moved leftward into the casing whereas positive values indicate the rod was being moved to the right out of the casing.

y = -1.9333x

-7

-6

-5

-4

-3

-2

-1

0

0 0.5 1 1.5 2 2.5 3 3.5


(volts)



y = 30x

-80

-60

-40

-20

0

20

40

60

80

-3 -2 -1 0 1 2 3

LVDT Output (volts)


Voltage Ouput vs. Displacement

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Table Appendix

Station A:

Dimension Measured Value (inches)

Length 6 Width 1 Height 0.121

Table 1: Featured here are the dimensions for the aluminum bar sample. The height

was measured using a digital micrometer.


Length 4.5 Width 2.5 Height 0.035

Table 2: Shown above are the dimensions for the aluminum plate sample. The height




Table 3: Shown above are the dimensions for the steel sample. The height was

measured using a digital micrometer.


Length 4 Width 3.75 Height 0.405

Table 4: Shown above are the dimensions for the wood sample. The height was


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Station C:



Table 5: Shown above are the dimensions for the aluminum plate sample. The height



Length 4 Width 3.75 Height 0.4

Table 6: Shown above are the dimensions for the wood sample. The height was


Station F:


Length 4.875 Width 3.875 Height 0.125

Table 7: Featured here are the dimensions for the steel plate sample. The height was




Table 8: Featured here are the dimensions for the square wood sample. The height


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Displacement Sensors Lab Report